Electric arc electrode



. oz zoo mw 35%?. O L :om 0 @zaoazoo/ NEL.; r 2 U e @l O O d n m m o A R7 E m w nmazx u E M U m m M A n mmm: A. F I m m .60mm N L m53 m y @zwzmm ma.; o @2:8200 mmm: E 33%2 95228 5 o Szmd @2352! Oct. 4, 1960INVENTOR ALBERT MULLER I 00am ATTORNEY ELECTRIC ARC ELECTRODE AlbertMuller, Watchung, NJ., assignor to Air Reduction Company Incorporated,New York, N.Y., a corporation 'of New York Original application May 17,1952, Ser. No. 288,447,

now Patent No. 2,694,763, dated Nov. 16, 1954. Divided and thisapplication Sept. 1'6, 1954, Ser. No. 456,448 v The terminal portion ofthe term of the patent subsequent to Nov. 16, 19171, has been disclaimed2 Claims. (Cl. 117-202) This invention relates to gas shielded electricarc welding and more particularly to electrodes for use in inert gasshielded arc Welding with a consumable or depositing electrode, referredto herein as inert gas shielded metal arc welding.

This application is a division of my co-pending application Serial No.288,447, filed May 17, 1952, now Patent 2,694,763, which is in somerespects a division and in other respects a continuation-in-part of mycopending application Serial No. 204,726 tiled January 6, 1951, which inturn is a continuation-impart of my prior application Serial No. 76,443,tiled February 15, 1949. The inventive subject matter hereof can beconsidered in at least certain aspects to constitute a new and usefulimprovement in electrodes for gas shielded metal arc Welding of the typedisclosed in Muller et al. Patent No. 2,504,868, issued April 18, 1950;Miksalapov Patent No. 2,544,711, issued March 13, 1951; and Muller etal. Patent No. 2,544,801, issued March 13, 1951; all assigned to theassignee of the present application.

In general, this invention involves the addition to an inert gasshielded consumable electrode welding arc of a substance or substanceswhich act to alter, in a desired predetermined manner and to a desiredpredetermined extent, the heat balance between the welding electrodes,i.e., the quantity of heat released or produced at the cathode duringthe welding operation relative to the heat released or produced at theanode during the welding operation. Thus the heat balance of the inertgas shielded metal arc welding process can be controlled. Further and/orother features hereof involve the addition to such a welding arc of asubstance or substances which act to improve the characteristics of themetal transfer from the consumable electrode to the workpiece; toimprove the stability of the arc, and to control or alter in a desiredmanner those factors of the welding arc which determine the speed,eiliciency and facility of the welding Operation and the characteristicsof the resulting weld.

Patents Nos. 2,504,868; 2,544,711; and 2,544,801 referred to above,disclose a welding operation of the type in which a consumable electrodewire is fed continuously to a gas shielded welding arc maintainedbetween the electrode and a workpiece (plate), the welding currentsupplied to the arc being at least sufficient to consume the electrodeas it is fed to the arc and transfer weld metal from the electrode to aweld deposit on the workpiece to form a commercially satisfactory weld,the current preferably being also supplied at a high current densitysufficient to provide a smooth, fast and uniform deposit or spray typetransfer (see Patent No. 2,504,868) of said electrode metal to the welddeposit. The shielding gas consists essentially of an inert gas. lnertshielding gas as used herein refers to the monatomic gases or mixturesthereof such as helium and/or argon and may include minor proportions ofother gases that United States Patent() ICC do not substantially alterthe shielding characteristics of said monatomic inert gas or gases,preferably supplied as a substantially non-turbulent or laminar owstream of suthcient flow stiffness to exclude substantially all the`ambient atmosphere from the arc. Such an arc involves an electricaldischarge through a controlled gas atmosphere. The gas in the arc gap isionized and the resulting positive gas ions are impelled by thepotential gradient toward the cathode where they yield their energy tothe cathode or are neutralized by electrons emitted from the cathode.Metal vapor formed in the arc region by vaporization of the electrode,the plate (workpiece) or any other source such as a separate fillerwire, forms part of the gas in the arc gap, so that the arc atmosthecase in welding in air, under a ilux blanket, or with.

coated electrodes, the characteristics of such an arc, at a constantpressure, depend solely upon the characteristics of the plate andelectrode metals and of the inert shielding gas.

According to the present invention, it has been discovered that byproviding certain addition substances in said arc (in addition to themetal which is melted to form the weld bead and the metal vaporsthereof, and in addition to the inert shielding gas) the heat balanceand/or certain other characteristics of the welding arc can becontrolled or changed in a desirable manner. These addition substancesare so selected and so added to the arc as to lower the work function ofthe cathode to shift the heat balance (the heat generated or released atthe cathode relative to the heat generated or released at the anode) ina predetermined manner and to a predetermined extent, and to provide astable, concentrated cathode spot. It is believed that where the wire isthe cathode concentration of the cathode spot in this manner improvesmetal transfer so long as the drops or spray of molten metal as itleaves the wire is completely immersed in the plasma. rIlhus, theaddition materials of the present invention may act to stabilize the arcand improve the metal transfer characteristics of the arc (for example,promote the spray type transfer from the wire to the Work), also theymay alter in a predetermined manner such factors as wire burn off rate,penetration, and size and contour of the weld bead.

It is believed that the heat liberated or generated at the cathode ininert gas shielded metal arc welding is to a large extent the result ofthe positive ion bombardment thereof. When the cathode is of such naturethat it emits electrons thermionically in relatively large quantities atits welding temperature, it is believed that the positive ions areneutralized to a large degree before they reach the cathode, the cathodevoltage drop is low, and bombardment of the cathode and generation of'heat at the cathode is minimized. When the cathode is a poor thermionicelectron emitter at its welding temperature, the positive ionbombardment is heavier, the cathode voltage drop is high7 and relativelylarge quantities of heat are generated at the cathode.

It has 'been found that when a material which is a good thermionicelectron emitter at its welding temperature (i.e., a thermionicmaterial) is used as ya welding arc cathode it forms `a very etiicientcathode with a low cathode voltage drop and a low heat release. This maybe attributed to the fact that positive ion bombardment which is thoughtto produce a major portion of the total heat liberated to lthe cathodeis relatively light, or limited, in the case of thermionic materials;such materials emit at their welding temperature, with a low cathodevoltage drop, all the electrons needed by the arc. This limiting effectis not present in the case of the relatively poor thermionic emitters orcold cathode materials, in which class fall most of the commonstructural materials such as aluminum, copper, nickel, iron, magnesium,titanium, etc., and alloys thereof normally welded commercially in largequantities. From a highly simplified viewpoint, if cold cathode materialis used as the cathode of the arc it forms an inefficient cathode and asa result, there is in the inert gas shielded welding arc havingelectrodes of cold cathode material a heavy positive ion bombardment ofthe cathode and a nigh heat release at the cathode, as compared withcathodes of thermionic material which are relatively efficient,resulting in a low heat release.

There is little difference in the heat release to the welding arc anode,whether it be composed of a thermionic or a cold cathode material. lthas been found that the anode heat release is intermediate between thehigh heat release to a cold cathode material used as a cathode and athermionic material used as a cathode.

There is another important difference between `the operation of athermionic cathode as compared to a cold cathode in inert gas shieldedmetal arc welding. Since the -thermionic cathode emits electrons readilyand copiously by virtue of its temperature, it continues to emit theseelectrons even after the current to the arc is eX- tinguished due to thethermal lag in the temperature of the electrode. Since electron emissionby cold cathode material does not depend upon thermal effect, the supplyof electrons is immediately extinguished when the current isinterrupted. lt has been found that thermionic materials form morestable inert gas shielded consumable electrode welding' arcs,particularly when A.C. is used fo-r the power supply. When `arcinterruptions occur a supply of electrons continues to be given oi fromthe thermionic cathode by virtue of its temperature tol produce easyire-ignition of the arc at a low open circuit voltage. The cold cathodematerial requires a very high open circuit voltage, sufficient toestablish a glow discharge, before ire-striking the arc after an arcinterruption.

The present invention provides for the modification of welding electrodematerials, and particularly cold cathode welding electrode materials, ininert gas shielded metal arc welding to produce electrical and thermalarc characteristics that are similar to and/ or which approach to apredetermined degree the electrical and thermal arc characteristics ofthermionic welding electrode materials, at the temperatures occurring inthe inert gas shielded consumable electrode welding arc. The electricaland thermal characteristics of an inert gas shielded metal welding arcbetween electrodes formed of cold cathode materials are thus controlled,such control being accomplished preferably through the addition ofmaterial to the arc which acts to change the heat produced or releasedat the cathode relative to that produced or released at the anode, i.e.,4to shift the heat balance of the arc. It has been found that suchadditions may be made in minute amounts relative to the amount ofdeposited weld metal, or electrode wire consumed. The material added maybe in such small amounts as to affect only the eleotrical and thermalcharacteristics of the arc. While it will change beneficially or controlthe size and shape of the weld bead it can, if desired, be so selected,and used in such small quantities, as to have no substantial orappreciable effect on the chemical composition of the weld metal, or`appreciable reaction with the metal being welded.

Welding arcs to which additions are made according to this invention arepreferably those having a substantially sterile arc iatmosphere orenvironment consisting essentially of inert shielding gas and such metalor like vapor as boils off the electrode, and workpiece. Thenon-turbulent inert shielding gas stream substantially excludes theambient atmosphere from such welding arc and, because the weldingprocess is a iluxless one, the electrical and thermal characteristics ofsuch arcs depend solely upon those of the shielding gas and the metal ofthe electrodes. Fluxless, sterile, consumable bare electrode weldingarcs of this character have different electrical and thermal propertiesthan welding arcs in air, welding arcs formed under `a submerged liuxblanket, or those formed with the conventional fluit coated electrodes.It has been found, according to the present invention, that theelectrical and thermal characteristics of such inert gas shieldedconsumable electrode welding arcs can delibenately be varied andcontrolled to provide new :and improved types of welding. The relativelypure, sterile inert gas environment insures that the added controlsubstances will act upon or with, or will modify the arc electrodesurfaces and/ or the arc atmosphere in the manner and to the extentdesired without loss of the beneiicial effect of the inert shielding gasand without either loss of control or undesired further modification ofelectrical and thermal properties that might result from the presence ofimpurities such as air or fluxes and coatings which are present inconventional welding in air, under a flux blanket, and with coatedelectrodes.

One ofthe objects of the invention is to provide a commerciallypnacticable means for shifting the heat balance of the inert gasshielded consumable electrode direct current welding arc to a selecteddegree. Direct current welding arcs are, of course, of two types, thestraight polarity direct current welding arc in which the wire electrodeis the arc cathode and the reverse polarity direct current welding arcin which the plate or work is the larc cathodef Another object is toprovide means for improving the metal transfer characteristics and thestability of the inert gas shielded consumable electrode direct currentwelding arc and the inert gas shielded consumable electrode alternatingcurrent welding arc.

Other objects are to obtain better arc stability in inert gas shieldedmetal arc welding, particularly where inert shielding gases ofrelatively poor ionization properties, such as helium, are used; and toprovide means for varying or controlling such factors of the inert gasshielded consumable electrode welding arc as weld bead size, shape andpenetration, rate of weld metal deposition from the consumable electrodeto the plate (burn off rate), amount of plate metal melted per unit oftime, size and shape of the weld crater and the Weld puddle on theplate, and similar factors having to do with the speed, facility ofoperation and results of the inert gas shielded metal arc weldingprocess.

Still other objects, results and advantages of the invention will beunderstood by and apparent to those skilled in the art upon consideringthe following detailed description and explanation of certain presentlypreferred embodiments of the invention and from the accompanyingdrawings in which:

Fig. l illustrates schematically a method and apparatus for makingadditions to a welding electrode wire for the purpose of the presentinvention.

Fig. 2 illustrates, on a somewhat enlarged scale, the welding wire as itappears during the various steps of preparation illustrated in Fig. l.

As previously stated, the invention can be utilized for the purpose ofcontrolling the amount of heat liberated at one terminal of an inert gasshielded consuming electrode welding arc relative to the heat liberatedat the other terminal of the same welding arc. In inert gas shieldedmetal arc welding of the common 'structural metals or cold cathodemetals, when the work is made the cathode of a direct current arc andthe consuming electrode wire is made the anode (i.e., reverse polarity),considerably more heat is liberated at the work than in the wire. By

providing certain materials in the arc in very small amounts and in themanner to be hereinafter more fully described, all other conditionsbeing the same, this invention enables the heat balance to be shifted inreverse polarity operations by any desired amount to the other extremecondition where the heat in the wire greatly exceeds the heat in thework. Similarly in inert gas shielded metal arc welding of the commonstructural metals where the wire electrode is made the cathode and thework'is made the anode (i.e., straight polarity) considerably more heatis liberated in the wire than is liberated in the work-this to theextent of making the process in many instances practically inoperable.By providing certain materials in the arc in amounts and in the mannerto' be hereinafter more fully described, all other conditions being thesame, this invention en- -ables the heat balance to be shifted by anydesired amount to make the process operable by reducing the heat in theWire relative to the heat in the work. By the proper selection andapplication of materials, a heat balance can be provided in the straightpolarity inert gas shielded metal arc welding process with heat balancecontrol additions that approximates the heat balance provided by thereverse polarity process with no additions present; straight polarityinert gas shielded metal arc welding can thus be made a commerciallysatisfactory process.

Example I For example, aluminuml can be welded with straight polarityaccording to the invention by making a cesium nitrate addition to thealuminum electrode wire, as shown by the following. A weld was made onan laluminum alloy plate with an aluminum alloy electrode, using weldinggrade argon (99.5% pure) as a shield gas delivered as a non-turbulentflow stream at 7S cubic feet per hour through a 1 inch diameter nozzle.The apparatus was substantially the same as that disclosed in theaforementioned Mueller et al. Patent Number 2,504,- 868. The electrodewire was a lAG inch diameter 43 S aluminum wire having applied thereto asmall amount of cesium nitrate. The plate on which the weld bead wasdeposited was 61 ST aluminum @As inch thick. The weld travel speed was linches per minute. The cesium nitrate was applied to the wire (Figs. land 2). The wire was first prepared by passing it through a pair ofrolls, one of which was knurled, to form transverse impressions (about.005 inch deep and spaced apart by about 1/32 inch) on its surface (Fig.5). The cesium nitrate, in the form of a dry powder, was made into aslurry or paste by mixing it thoroughly with a quantity of denaturedalcohol. This slurry or paste was then applied to the wire by brushingit onto the surface (Fig. l) and into the transverse impressions on thewire surface. Following this step the wire was passed through atightlytting annular rubber squeegee to remove the excess slurry. Nextthe wire was passed through a pair of smooth surfaced semi-circularlygrooved rolls to smooth the surface roughness caused by the knurled rolland trap some of the addition material in the impressions. The surfaceof the wire was then wiped with a clean dry cloth to removesubstantially all the cesium nitrate except that which was trapped orimpressed by the above treatment into the electrode surface. The alcoholevaporated leaving the wire dry. When prepared in the manner described,

the Wire has a substantially bare, electrically conductive surface andit can be readily fed through the welding apparatus; its'ability to pickup the welding current from the contact tube is unimpaired. Under theaforesaid conditions and with an arc current of 220 amperes, straightpolarity, the Wire burn olf rate (wire feed speed) was 160 inchesV perminute and the arc voltage 16 volts. The

weld operating conditions were excellent with spray translength andvoltage remained substantially constant). The weld bead was well roundedand smooth.

To illustrate the eifect in heat balance shift produced by this additionof cesium nitrate to the aluminum electrode wire a comparable straightpolarity weld was attempted with an untreated aluminum electrode. Thesame apparatus and identical welding conditions were used with theexception 'that an untreated aluminum electrode was substituted for thecesium nitrate :treated electrode. The resulting process was inoperable.The burn off rate was excessive, being well over 500 inches per minute.There was very poor arc regulation, the arc was wild and spatterprofuse. The weld bead was irregular and not well fused into the platebut rather overlapped the plate and lacked adequate penetration. The arcvoltage was considerably higher than that with the cesium nitratetreated wire, but because of the poor arc length regulation it wasimpossible to obtain a reliable arc voltage reading. The significant andconclusive difference between the process with the cesium nitratetreated Wire and the untreated wire is that in the rst the wire burn olfrate was inches per minute whereas in the second it was in excess of 500inches per minute, indicating a vast difference in the amount of heatliberated in the wire as a cathode. In addition, transfer of metal inthe first case was good and the process a commercially operable process,whereas in the second, transfer was poor and the process inoperable forpractical purposes.

Example II The following is a further example of the application of theinvention to non-ferrous metals. Welds were made on a steel plate usingan aluminum bronze alloy wire electrode, both with the wire treated withcesium rubidium chloride and with an untreated wire. The particular wireemployed was an alloy comprising approximately 9% aluminum and thebalance copper. The wire was 1A@ inch in diameter, and the plate onwhich the weld bead was made was inch thick mild steel. The weldingapparatus and the gas shield were identical to those heretoforedescribed. Cesium rubidium chloride was applied to the electrode wire inexactly the same manner as the rubidium carbonate in the iirst examplein this specification. With the electrode wire connected as the cathode(straight polarity), and a welding current of 225 amperes, the treatedwire burn off rate was 210 inches per minute at an arc voltage of 18volts. Metal transfer across the arc was good, being in the form of afast drop transfer. The bead was quite well faired into the plate andhad an oval profile. Arc length regulation was good. When identicalconditions were maintained, but an untreated wire employed, the burn olfrate was 320 inches per minute at an arc voltage of 20 volts. The metaltransferred across the arc in larger drops, the bead formed wasirregular, and there was poor regulation of the arc. The deposited metalbuilt up on the plate and did not fuse in well. The process wasinoperable from a practical point of View. Again, it may be seen thatconsiderably more heat was liberated in the wire as a cathode when thewire was untreated, as compared with the heat liberated in the wirehaving small quantities of cesium rubidium chloride associatedtherewith.

While heat balance shift is probably easiest to statistically `describein `connection with rthe straight polarity arc because of the extremedifferences in wire burn off rate, it is also present in the reversepolarity arc. As stated above, heat liberated at the anode of thewelding are is practically independent of the emissivity of the anodematerial, therefore the wire burn off rate should be substantiallyconstant with reverse polarity (wire the anode) whether or not theadditions of the present inven-v This has been found to be tion are madeto the arc. true.

Example III Another example, using reverse polarity, with a non- 17ferrous material, is a weld made with a /l, inch diameter aluminumelectrode wire, utilizing the same welding apparatus hereinbeforedescribed. The gas shield was welding grade argon delivered at 75 cubicfeet per hour in a non-turbulent ow through a 1 inch diameter nozzle. A3%3 inch thick aluminum plate was the cathode. When the wire was irsttreated by applying a small amount of cesium nitrate in the mannerpreviously described the wire burn oif rate was 165 inches per minute at205 amperes and 19 volts. The resulting weld was good. When an untreatedaluminum wire was used under the same circumstances the wire burn offrate was 175 inches per minute at 22 volts. The weld bead was somewhattiatter and the arc characteristics and metal transfer were good.

It is significan-t to note that when the wire is the anode the additionmaterial has little or no effect on the wire burn olf rate but the arcvoltage is reduced by a substantial amount and the total arc power isconsiderably less. Since the wire burn off rate is substantiallyconstant, it is evident that the heat in fthe Work rnust be reduced.This is exactly what would be expected according to the invention if thework were made a better thermionc emitter. Therefore, it is clear thatin these reverse polarity examples the addition made to the wiretransferred to the weld pool with the depositing weld metal andincreased the thermionic emission of the weld pool as a cathode. Thus,when additions are made to the Wire according to the invention the heatliberated in the wire is substantially reduced where the wire is thecathode and the work the anode, and the heat liberated in the work canalso be substantially reduced Where the wire is the anode and the workthe cathode.

lt has been found that very small amounts of the addition materials arerequired to effect the desired results. It is clear from'the precedingdescription of a method of application of the material to the Wire whichhas been found satisfactory, that very little of the addition materialremains on the wire in its finished, treated state. As a matter of fact,diiculty may be encountered in feeding the wire through the contact tubeyand transferring current to it if the added material is on the surfaceof the wire in sufficient quantity fto rub off. The treated wire canstill be considered as a bare Wire, and its surface is electricallyconductive for pick-up of the Welding current as it is fed through thecontact tube.

The addition materials of the present invention are materials that breakdown (if a compound) into a metallic emission agent or element, of lowwork function and low ionization potential, which is electropositivewith respect to the cathode base metal and which provides a thin ilmover all or part of the electrode (cathode) surface during the weldingoperation. The coating of an electro-positive metal on a moreelectro-negative one produces a marked lowering of the work function ofthe composite surface, resulting in effect in increased thermionicemission at welding electrode temperature. The process is believed toproceed kas follows. The compound containing the emission agent orelement (assuming the emission iagent is added to the are in the form ofa compound) is reduced or dissociated and frees the emission agent as ametal in or on the molten portion of the welding cathode. r[The emissionelement diffuses to the molten cathode surface and/ or migrates oversaid surface to form a composite, highly thermionically emissive,welding cathode surface. It appears that the fully activated surfacecorresponds to a monatornic layer of atoms or ions of the emissionagentwhich covers a large part, for example more than 50% of the cathodesurface. This thin layer of the emission element is held on the surfacewith attractive forces so strong that substantial evaporation does notbegin until temperatures are reached that are well above the boilingpoint of the emission element, though excess quantities of the elementmay evaporate at lo-w temperatures to leave said thin layer or patchesof the element on the cathode surface. It should be noted that thetemperatures of the welding arc, usually operated atatmosphericrpressures, are above the dissociation points of mostcompounds. The monatomic layer or patches of atoms of the emissionelement is believed absorbed as ions on the base metal cathode surfaceand the forces which tend to hold it in place should be highest when theionization potential of the emission element is low, it would appearthat the ionization potential of the emission element should be lessthan the work function of the cathode base metal but in practice,possibly because work functions are diicult to determine accurately, ithas been found that the ionization potential of the emission metal maysometimes be as high as one and one-half electron volts greater than thevalues given by reliable investigators for cathode base metal workfunctions. In general, the emission element must be electropositive withrespect to the base metal; the work function of the composite surface islowest and its thermionic emissivity is highest when this difference isat its largest positive value and the work function becomes higher andthermionic emissivity lower as the difference reaches zero and becomesnegative.

As an Ialternative to the preparation method of Fig. 1, in which thematerial is applied to the surface of the Wire or embedded in surfaceindentations therein, the addition material may be added to the meltwhen the wire is being manufactured, to form an alloy or mixturetherewith. This provides homogeneous distribution of the additionmaterial through the wire and eliminates the need for separateprocessing of the wire subsequent to its manufacture in wire form.

Beside the `above-described modes of introducing the addition materialto the arc for the purposes herein described, it has been found thatunder certain conditions the addition material can be put on anauxiliary filler wire that is fed to the Weld, or the addition materialmay be placed on the work directly.

While certain specific examples and embodiments of the invention hasbeen described above for the purpose of illustrating its nature andoperation, it is to be understood that the invention may also beutilized and practiced by those skilled in the art in other ways withoutdeparting from its spirit or scope as defined by the following claims.

I claim:

l. A consumable inert gas shielded metal arc welding electrode formedwith a bare electrically conductive surface, said electrode consistingessentially of aluminum and having an arc control addition thereto of acompound of cesium.

2. A consumable non-ferrous inert gas shielded metal arc-weldingelectrode comprising essentially a metal selected from the groupconsisting of aluminum, copper, nickel, tand magnesium and formed with asubstantially bare electrically conductive surface and having an arccontrol :addition thereto of a compound of cesium.

References Cited in the file of this patent UNITED STATES PATENTS1,783,013 Green Nov. 25, 1930 1,817,448 Ulrey Aug. 4, 1931 1,916,206Dawson July 4, 1933 1,936,349 Castle Nov. 2l, 1933 1,976,397 Holst etal. Oct. '9, 1934 2,056,660 Foulke Oct. 6, 1936 2,219,872 Myers Oct. 29,1940 2,264,717 Ruedy Dec. 2, 1941 2,470,763 Doyle May 24, 1949 2,540,811Cobine Feb. 6, 1951 2,632,080 Wasserman Mar. 17, 1953 2,694,764 MullerNov. 16, 1954

1. A CONSUMABLE INERT GAS SHIELDED METAL ARC WELDING ELECTRODE FORMEDWITH A BARE ELECTRICALLY CONDUCTIVE SURFACE, SAID ELECTRODE CONSISTINGESSENTIALLY OF ALUMINUM AND HAVING AN ARC CONTROL ADDITION THERETO OF ACOMPOUND OF CESIUM.